1. Field of the Invention
The present invention relates to a trapping technique applied to a boundary portion where two different colors are adjacent each other in an image that is configured by allocating a plurality of figures having a relative upper and lower position order.
2. Description of the Background Art
There has heretofore been known the technique of forming an image on a printing paper by multicolor printing by using a plurality of press plates, which correspond to respective colors (process colors), such as C (cyan), M (magenta), Y (yellow), and K (black), and special colors.
In the image formed by such a multicolor printing, there is a boundary portion where two different colors are adjacent each other. In cases where when an image is transferred from press plates to a printing paper, a drift occurs at the positions of the press plates that correspond to respective colors, or expansion and contraction occur in the printing paper, there arises the disadvantages that a gap is left in this boundary portion and the paper color of the printing paper peeps out, and the like.
In order to avoid such a gap, “trapping process” has heretofore been performed in a prepress step. Trapping process is executable by allocating, for example, along a boundary portion where two colors are adjacent each other on an image, a narrow figure (hereinafter referred to as a “trap figure”) composed of the color components of the two colors.
Recently, the editing process of images in the prepress step is often performed on a computer. A series of steps relating to trapping process are also implemented by executing a predetermined program on a computer.
When performing editing on a computer in a prepress process, in some cases, an image (page) is handled as data obtained by allocating a plurality of figures to predetermined positions. Between the plurality of figures, the order of relative upper and lower positions (the front and the rear on the page space) are designated in some cases.
However, there are various methods of determining as to which color an overlapped portion is to have on an image, when a certain figure is allocated so as to overlap in its upper part with other figure. For example, there are the following methods: “knock out” that employs the color of the upper figure with regard to the color of the overlapped portion; and “overprint” in which the color of the upper figure is overlaid on the color of the lower figure to obtain a combination color of the two. Alternatively, there is the method of “irregular overprint” that employs a combination color of the colors of both figures only under regular requirements, and employs the color of the upper figure in other cases.
Depending on which one of these various methods is to be applied to, there arises a difference in the need for trapping process with respect to an adjacent boundary portion between the color of the overlapped portion of two figures and the color of the lower figure. In addition, when performing the “irregular overprint,” there arises a difference in the need for trapping process even by the color relationship of two colors allocated so as to overlap with each other.